How to identify mysterious physics force affecting my objects?
The mysterious invisible force is 12 copies of your ragdoll. They are not in your scene but in your blend file. It looks like these lost objects are still used for collision detection.
To get rid of the copies, select Blender File as Display Mode for the outliner. Look for Objects and expand it. If you select everything in the viewport, then you can easily see in the outliner which objects are used in the viewport. Delete the other unwanted copies.

If you want to see the hidden copies, create a new file, delete everything and use File → Append ... to append the collections RigidBodyContraints and RigidBodyWorld from this file. These collections are used internally by Blender and are connected to the lost objects. This way you can append them easily to your scene.
Revealing the 12 hidden ragdolls